EFFECTS OF PARA-CHLOROPHENYLALANINE (PCPA) ON THE BUSH-BABY AUDITORY BRAIN-STEM RESPONSE

Click-evoked auditory brainstem responses were recorded in a prosimian primate, the bush baby (Otolemur garnettii), before and after depleti on of serotonin (by systemic injection of pain-chlorophenylalanine; pC PA) and up to 20 days after discontinuing pCPA injections (during the recovery of serotonin). Biphasic 100 mu s clicks were presented at fiv e repetition rates (13.2, 33.2, 53.2, 73.2, and 93.2 clicks/s; RATE) a nd sound pressure levels (SPL) were varied in 10 dB steps from 120-60 dB SPL peak equivalent. Absolute latencies of vertex-positive peaks I, III, IV, and V were measured from click onset. The latencies from eac h wave were statistically analyzed with a two-way analysis of variance using either RATE or SPL (but not both) and TIME AFTER pCPA as indepe ndent variables. Prior to pCPA, brainstem response latencies increased as a function of both decreasing SPL and increasing RATE. After pCPA, these normal increases in wave latency increased even more, particula rly in response to high click rates. After pCPA was discontinued, meas urements taken at weekly intervals indicated that latencies decreased after 1 week, increased to the highest values recorded after 2 weeks, and returned to normal after 3 weeks. These dynamic changes were inter preted to be the result of postsynaptic receptor up-regulation during the 10 days of continuous pCPA administration. These results suggest t hat serotonin plays an important role in sensory processing at the cel lular level and, ionically, facilitates the auditory brainstem respons e to sound. (C) 1998 Published by Elsevier Science B.V.